Welcome to Seven Forums Andacar. Try this as a start. Download Lock Hunter:
Lock Hunter
Install Lock Hunter. This will add an entry to your right click context menu called
What is locking this file?
Next time you get the in use error, right click the file, and choose What is locking this file? It will tell you what process is locking the file. this may help us figure out why it is happening. Or, you can use Lock Hunter to unlock the file, and move it. A Guy